I'd like to get a extract table result, with a reference id primary key, showing the maximum dates for events and who was responsible for them. I can get the max(date) field in columns using PIVOT, but can't see a way to get the 'who' field without lots of LEFT JOINs.
Here's some test data and code which shows the principle:
CREATE TABLE #t
(
ref INT ,
id INT ,
who VARCHAR(10) ,
checkin DATE
)
INSERT #t
( ref, id, who, checkin )
VALUES ( 123, 1, 'andy', '2014-1-16' ),
( 123, 1, 'bill', '2014-1-17' ),
( 123, 1, 'carol', '2014-1-18' ),
( 123, 2, 'diana', '2014-1-16' ),
( 123, 2, 'andy', '2014-1-18' ),
( 123, 3, 'bill', '2014-1-16' ),
( 123, 4, 'carol', '2014-1-17' ),
( 123, 4, 'diana', '2014-1-16' ),
( 456, 2, 'diana', '2014-1-17' )
SELECT res.ref ,
[1] , who1 ,
[2] , who2 ,
[3] , who3 ,
[4] , who4
FROM ( SELECT ref ,
[1] , [2] , [3] , [4]
FROM ( SELECT ref ,
id ,
checkin
FROM #t
) src PIVOT ( MAX(checkin) FOR id IN ( [1], [2], [3], [4] ) ) pvt
) res
LEFT JOIN ( SELECT ref ,
who AS who1 ,
MAX(checkin) AS checkin
FROM #t
WHERE id = 1
GROUP BY ref ,
who
) one ON res.[1] = one.checkin
AND res.ref = one.ref
LEFT JOIN ( SELECT ref ,
who AS who2 ,
MAX(checkin) AS checkin
FROM #t
WHERE id = 2
GROUP BY ref ,
who
) two ON res.[2] = two.checkin
AND res.ref = one.ref
LEFT JOIN ( SELECT ref ,
who AS who3 ,
MAX(checkin) AS checkin
FROM #t
WHERE id = 3
GROUP BY ref ,
who
) three ON res.[3] = three.checkin
AND res.ref = one.ref
LEFT JOIN ( SELECT ref ,
who AS who4 ,
MAX(checkin) AS checkin
FROM #t
WHERE id = 4
GROUP BY ref ,
who
) four ON res.[4] = four.checkin
AND res.ref = one.ref
DROP TABLE #t
The result set is:
ref 1 who1 2 who2 3 who3 4 who4
123 2014-01-18 carol 2014-01-18 andy 2014-01-16 bill 2014-01-17 carol
456 NULL NULL 2014-01-17 NULL NULL NULL NULL NULL
Is there some way to avoid all the LEFT JOINs, may be by using another PIVOT, to produce the same result?
PS: How do I insert a table here? I tried HTML and it got stripped out!
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